My data shows that a steadily rising boiler wall temperature is needed to maintain a flat (or slightly dropping which is what I prefer) coffee temperature profile during brew. I'm measuring boiler wall temp at the top of the boiler, but I don't know that that differs much from anywhere else.

Perhaps I can look at your statement in reverse. I show a reasonably flat intrashot temperature so if your theory and data is correct and a steadily rising boiler temperature is necessary, then I must have one :)

Actually, AndyP used a boiler wall thermistor to develop his technique of flipping the steam switch. Yes, there was a fairly stable rise to about 235F where it somewhat levelled, IIRC. There is likely a similarly dampened temperature zone in front, on top and back on the boiler about equidistant from the heaters. He used the front and I used the top with similar results and numbers.

I initially used a Polder on the boiler top. Temperature does rise and appears more stable than the PID display. Again, by recall to about 235F. The PID displays temperature at the sensor, placed for maximal change and responsiveness, and the area of boiler between the heaters damps a fair amount as does the water, until the water temperature at group exit is mostly damped and stable. You may have the ability to measure and datalog all points at once and plot overlying. Actual temperature and damping at a given point probably do not matter much except in the data plots. Of course data helps to understand offsets, fluctuations, and to adjust that cup temperature. The PID display/responsiveness and the thermofilter, even damped, get you in the range. After that you need to adjust by the cup, by taste.

jonr Said:

It would be very interesting if someone sold a PID controller that could be programmed to ramp temperature at a specified rate. Or just switch to a defined power level (a constant 40% during brew works pretty well).

Not sure how that would actually help, but it is another way to approach the problem. AndyP did a manual method heavy on learning, technique and timing. The PID and SSR use full power but short intervals to arrive at a set, ShortyJacobs used PID and PWM to lower the power somewhat as you suggest, and you have computerized. All the methods seem to work. I guess it is up to reader to decide which is cost effective, understandable, and within their ability.

It would be very interesting if someone sold a PID controller that could be programmed to ramp temperature at a specified rate. Or just switch to a defined power level (a constant 40% during brew works pretty well).

Interesting. I checked the numbers with the simple temp profile I am currently using and the boiler wall rises from 104.0C to 116.3C during brew in an almost perfectly straight line. But given the delays in response time (roughly 4 sec), it might take some effort to get a PID controller to accurately control to this using the ramp function. Even harder to some non straight-line function.

My data shows that a steadily rising boiler wall temperature is needed to maintain a flat (or slightly dropping which is what I prefer) coffee temperature profile during brew. I'm measuring boiler wall temp at the top of the boiler, but I don't know that that differs much from anywhere else.

It would be very interesting if someone sold a PID controller that could be programmed to ramp temperature at a specified rate. Or just switch to a defined power level (a constant 40% during brew works pretty well).

MJW and Jonr, I started with a 1/32 din PID with one alarm and used added brew heat instead of steam, thinking that steam was easy enough without PID alarm control. When I realized that I wanted steam control also I started looking at 1/16 din with 2 alarms or Ramp soak. I had some email discussion with Suyi at Auber. Ramp could have done a single button preheat 3+ seconds, then rest 3+ seconds for preheat, and then start the pump and brew heat. I do not think that it offers much other advantage for this use. The thought is that you could make a few ramp step and keep upping the heat. I decided against that as I had already used brew heat and it worked. When I started I did not have other monitors and a way to prove that adding brew heat worked. AndyPanda and I happened to be doing similar at the same time, AndyPanda manually with the steam switch. The difference was his use of the Polder thermometer, a K thermocouple over the PF lip, and eventually a thermofilter.

When I changed to the 1/16 din PID I had the first PID available to use for a thermocouple monitor, and had already used AndyPanda’s Polder idea. What I found is that the boiler temperature does not vary like the PID controller sensor at the old boiler stat position. The boiler stat, and PID RTD sensor, was placed to be sensitive. The upper/top boiler temperature showed a steady rise similar to the boiler heated by flipping the steam switch.

jonr Said:

Interesting. I checked the numbers with the temp profile I am currently using and the boiler wall rises from 104.0C to 116.3C during brew in an almost perfectly straight line. But given the delays in response time (roughly 4 sec), it might take some effort to get a PID controller to accurately control to this using the ramp function.

OK, Jonr, you got me curious and made me do some work. I repeated the boiler temperature today with a k thermocouple at the top of the boiler. PID set temperature at 214F and top of boiler at 213F with 30 minute preheat. Shots are 25 ml in 25 sec. Shot/thermofilter temperature of 199F. The boiler shows a smooth steady rise to about 233F in about 20 – 21 seconds and then 235F in the last 4 seconds. No datalog, just observed similar over several attempts. Second and third shot with 1 minute rest from end of shot to next shot showed the boiler top only dropped t about 220F and rose in similar pattern to about 240 – 241F. About 22F rise is quite similar to Jonr’s 12.6C rise. No ramp soak, just adding brew heat with the alarm function with an on and off, no PID algorithms. PID algorithms are too damped to help. The mass of the boiler and water seem to damp the blips of full power from steps to a smooth ramp up. This may be technically unsophisticated , but is is functional and easy.

I prefer to talk about brew temperatures (plural), but I can confirm that the boiler wall sensor/PID temp at start of brew is noticeably higher than any starting brew temperatures seen in the basket, even with a fast probe. So here is a question - where did the extra heat go? Is the boiler wall temperature at the sensor higher than the water inside before brew starts? Or is the starting water temp ~214F and the cooler group is dissipating that much heat as the water flows from the boiler, through the group and into the basket?

MJW and Jonr, I started with a 1/32 din PID with one alarm and used added brew heat instead of steam, thinking that steam was easy enough without PID alarm control. When I realized that I wanted steam control also I started looking at 1/16 din with 2 alarms or Ramp soak. I had some email discussion with Suyi at Auber. Ramp could have done a single button preheat 3+ seconds, then rest 3+ seconds for preheat, and then start the pump and brew heat. I do not think that it offers much other advantage for this use. The thought is that you could make a few ramp step and keep upping the heat. I decided against that as I had already used brew heat and it worked. When I started I did not have other monitors and a way to prove that adding brew heat worked. AndyPanda and I happened to be doing similar at the same time, AndyPanda manually with the steam switch. The difference was his use of the Polder thermometer, a K thermocouple over the PF lip, and eventually a thermofilter.

When I changed to the 1/16 din PID I had the first PID available to use for a thermocouple monitor, and had already used AndyPanda’s Polder idea. What I found is that the boiler temperature does not vary like the PID controller sensor at the old boiler stat position. The boiler stat, and PID RTD sensor, was placed to be sensitive. The upper/top boiler temperature showed a steady rise similar to the boiler heated by flipping the steam switch.

OK, Jonr, you got me curious and made me do some work. I repeated the boiler temperature today with a k thermocouple at the top of the boiler. PID set temperature at 214F and top of boiler at 213F with 30 minute preheat. Shots are 25 ml in 25 sec. Shot/thermofilter temperature of 199F. The boiler shows a smooth steady rise to about 233F in about 20 – 21 seconds and then 235F in the last 4 seconds. No datalog, just observed similar over several attempts. Second and third shot with 1 minute rest from end of shot to next shot showed the boiler top only dropped t about 220F and rose in similar pattern to about 240 – 241F. About 22F rise is quite similar to Jonr’s 12.6C rise. No ramp soak, just adding brew heat with the alarm function with an on and off, no PID algorithms. PID algorithms are too damped to help. The mass of the boiler and water seem to damp the blips of full power from steps to a smooth ramp up. This may be technically unsophisticated , but is is functional and easy.

The context of the above set up was to test boiler temperature rise at the top of the boiler away from the bstat location. I tried to mimic your work

jonr Said:

I checked the numbers with the simple temp profile I am currently using and the boiler wall rises from 104.0C to 116.3C during brew in an almost perfectly straight line. But given the delays in response time (roughly 4 sec), it might take some effort to get a PID controller to accurately control to this using the ramp function. Even harder to some non straight-line function.

I had a flat temperature at 199F in the basket, noted for your reference, and yes, of course it was made up of temperatures (pleural) as understood above.

jonr Said:

So here is a question - where did the extra heat go? Is the boiler wall temperature at the sensor higher than the water inside before brew starts? Or is the starting water temp ~214F and the cooler group is dissipating that much heat as the water flows from the boiler, through the group and into the basket?

You are the engineer, I can only speak from observation. We agree the PID sensor at the bstat location reads higher than the top of the boiler. The bstat screw is in the wall surrounded by the element and the top of the boiler is perhaps the farthest away from the elements you can get on the boiler. Already a couple of degrees accounted for, but the top of the boiler is also hotter than the group water temperature.

The blip of the heat prior to brew is to offset the lag of incoming cold water, instantaneous, opposed to heat that must go from the boiler shell into the water passively. It is not about system reaction delay as it still does not work just to turn on the heater with the pump as opposed to letting the controller sense change and then turn on heat. Because heat has to dissipate in, it needs a head start to the incoming cold, suggesting early mixing to me.

Cold water enters the bottom of the tank and hot exits off the top, but significant mixing of tempertures occurs very quickly, perhaps almost instantly to see the temperature drop in a non-temperature controller machine.

My PF/basket probe reads about 192 – 195F without flow, so some drop is going to be from mixing in the puck/simulator.

Todd’s, daduck748 thread may have some answers. He had a probe in the center of the boiler water, but I do not recall if he did bstat location, boiler water, and thermofilter all at the same time.

My final observation is that while I may not understand the reason for the bstat, or top of the boiler, temperature offset from the thermofilter puck water, I do understand that the offset is observed and I can set the PID controller to account for that and dial what hits the thermofilter and hopefully the puck. Perhaps while interesting, the reasons for the offset are not as important as dealing with the offset. Also, while I used the 199F flat setting above, I dial in a bit less heat and allow some drop in daily use as you do.

The primary reason for fully understanding the delta is when applying similar controls to other machines. Most have internal heaters (vs boiler wall), some have tubing running from the boiler to the group (more heat loss) and some have temperature probes inside the boiler. A few have a separate heater for the group.

But there is some applicability to the Classic. To the extent that the 15F delta is caused by heat loss to the surroundings, it changes with the surrounding (aka ambient) temp. For example, if room temperature changes from 78F to 68F, I'd expect a ~1F higher delta. And another 1 or 2F drop in the ending brew temp (if not thermostatically controlled) due to the lower temp of water coming into the boiler. Fine points, but others have shown clearly that 1 or 2F changes make a noticeable difference in taste.

Just finished PID'ing my Gaggia Classic. That was some serious fun! :) Thanks so much for all the time spent laying out the details for everyone! I ended up just going with the Auber SYL-1512 and using the alarm for steaming. I found using the steam switch for 4 sec before I pull my shot to be effective enough in giving me good brew temp throughout the pull. Went with the a la carte approach vs buying the kit and saved at least $75 or so. Everything I needed I got from Auber and the Shack. Works great! Fun project! Thanks again!

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